The present invention relates generally to sampling a body of molten metal for analysis purposes, and particularly to a method and apparatus for controlling the depth of a sampling wheel in a molten body or stream of metal that experiences changes in elevation in the upper surface of the body or stream.
Patent application Ser. No. 826,988, filed Feb. 7, 1986 now U.S. Pat. No. 4,783,417, issued Nov. 8, 1988, discloses a system in which the teeth of a serrated wheel are rotated in a source of molten metal to provide solid metal flakes, and apparatus in which the flakes are analyzed for elements of the composition of the metal of the molten source. The system, in addition, provides physical separation of the analytical apparatus from the harsh environment of the molten source. In this manner, the flakes formed at the location of the source by the serrated wheel are analyzed at a substantial distance from the source, the flakes being transported to the analysis apparatus by a gas stream flowing through a tube or conduit extending between the wheel and the analysis apparatus. Such a system and procedure allows analysis of molten metal before and during casting so that its alloy composition can be changed if required.
A problem encountered in using a sampling wheel in a body of molten metal is locating and maintaining the peripheral teeth of the wheel a precise depth in the molten body when the elevation of the upper surface of the body changes. If the lower teeth of the wheel are too deep in the molten metal, the wheel produces a wire of solidified metal, as opposed to particles or flakes. If the serrations do not enter the metal at a sufficient depth, an insufficient amount of metal adheres to the serrations such that an insufficient amount of particles is produced for sampling.
Changes occurring in the elevation of the molten surface can be gradual or abrupt. Gradual changes occur as filters, used to maintain the purity of the metal to be cast, become clogged, or when the head of the molten metal is changed at the casting apparatus, for example. Abrupt changes in the level of the metal in a casting trough can occur when a pouring operation begins, i.e., when metal is poured from a furnace that supplies the casting process with the molten metal. Pouring is effected by tilting the furnace, the angle of the tilt, and the rate of pour, being controlled by sensors that sense the level of metal in a pouring trough. The control effected by the sensors can cause an oscillating movement of the pouring process that causes waves in the upper level of the molten metal to be sampled.